So what's commonly considered 'broken'?
Ka'Tan and Ka'Toc arguably,
Tertius, Prefect and Salust,
most of the Minbari fleet,
most of the fast Dilgar esp. the Targrath,
the SFoS White Star,
the old tourney Shadow Hunter (fixed?)
and from Earth, only really the Sagittarius.
Under- powered or ineffective ships?
Raid level Narn and all the War level except the Bin'Tak,
most of the Skirmish level Centauri and some of the rest of the Raid ships,
the Drakh were, but most people who were interested seem to have got the hang of them now,
SFoS Vorlons and Shadows (fixed),
the Abbai lack range,
the Drazi lack manoeuvrability to bring their guns around,
the Vree lack toughness,
and the Raiders are just a lost cause.
Only one imbalanced ship to excuse another? There are an awful lot of them right there, and most of them function adequately and enjoyably- against each other. ISA-Dilgar, broken White Stars and all, is great fun, a real twisty- turny tactical manoeuvring game. The Centauri heavies are meant to suppress the Narn wolfpack and vice versa, and for that matter Centauri- Minbari is always good, firepower versus evasion.
No ship is balanced, when you look at it on it's own. In context, a lot of these supposedly bent ships start to work again.
The Saggy is still wrong, though.